visibility: fix a comment introduced before which is not up-to-date
265cd9e19d26 introduced a comment in _filterederror that was not updated with
the latest iterations of the patch, fix the comment.
Differential Revision: https://phab.mercurial-scm.org/D1851
#require docutils gettext
$ $TESTDIR/check-gendoc pt_BR
checking for parse errors